Shaped catalysts for transalkylation of aromatics for enhanced xylenes production

ABSTRACT

A catalyst, a process for using the catalyst whereby the catalyst effectively transalkylates C 7 , C 9 , and C 10  aromatics to C 8  aromatics are disclosed. The catalyst comprises a support such as mordenite plus a metal component. The catalyst provides an enhanced life and activity for carrying out the transalkylation reactions at relatively low temperatures. This is achieved by reducing the maximum particle diameter of cylindrical pellets to 1/32 inch (0.08 cm) or a trilobe to 1/16 inch (0.16 cm).

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Division of application Ser. No. 10/141,294 filedMay 7, 2002, now U.S. Pat. No. 6,815,570, the contents of which arehereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to catalytic hydrocarbon conversion, and morespecifically to the use of a catalyst for transalkylation of C₇, C₉, andC₁₀ aromatics to C₈ aromatics at relatively low temperatures. Saidcatalyst comprises a suitable solid-acid support such as mordenite,beta, MFI, silica-alumina or a combination thereof with or without asuitable metal element promoter such as platinum, germanium, or rhenium.The catalyst is extruded into either a trilobe with a maximum effectivediameter of 1/16 inch (0.16 cm) or cylindrical pellets with a maximumdiameter of 1/32 inch (0.08 cm).

BACKGROUND OF THE INVENTION

The xylenes, para-xylene, meta-xylene and ortho-xylene, are importantintermediates which find wide and varied application in chemicalsyntheses. Para-xylene upon oxidation yields terephthalic acid, which isused in the manufacture of synthetic textile fibers and resins.Meta-xylene is used in the manufacture of plasticizers, azo dyes, woodpreservers, etc. Ortho-xylene is feedstock for phthalic anhydrideproduction.

Xylene isomers from catalytic reforming or other sources generally donot match demand proportions as chemical intermediates, and furthercomprise ethylbenzene, which is difficult to separate or to convert.Para-xylene in particular is a major chemical intermediate with rapidlygrowing demand, but amounts to only 20–25% of a typical C₈ aromaticsstream.

Ethylbenzene generally is present in xylene mixtures and is occasionallyrecovered for styrene production, but usually is considered aless-desirable component of C₈ aromatics.

Among the aromatic hydrocarbons, the overall importance of the xylenesrivals that of benzene as a feedstock for industrial chemicals. Neitherthe xylenes nor benzene are produced from petroleum by the reforming ofnaphtha in sufficient volume to meet demand, and conversion of otherhydrocarbons is necessary to increase the yield of xylenes and benzene.Often toluene (C₇) is dealkylated to produce benzene (C₆) or selectivelydisproportionated to yield benzene and C₈ aromatics from which theindividual xylene isomers are recovered.

A current objective of many aromatics complexes is to increase the yieldof xylenes and to de-emphasize benzene production. Demand is growingfaster for xylene derivatives than for benzene derivatives. Refinerymodifications are being effected to reduce the benzene content ofgasoline in industrialized countries, which will increase the supply ofbenzene available to meet demand. Benzene produced fromdisproportionation processes often is not sufficiently pure to becompetitive in the market. A higher yield of xylenes at the expense ofbenzene thus is a favorable objective, and processes to transalkylate C₉aromatics and toluene have been commercialized to obtain high xyleneyields.

U.S. Pat. No. 4,857,666 (Barger et al.) discloses a transalkylationprocess over mordenite and suggests modifying the mordenite by steamdeactivation or incorporating a metal modifier into the catalyst.

U.S. Pat. No. 5,043,509 (Imai et al.) discloses a process for conversionof organic compounds with a phosphoric catalyst consisting of a shapedextrudate with a specific maximum ratio of length to diameterrepresenting the ratio of exterior surface area to catalyst volume.Shaped catalysts have also been described in U.S. Pat. No. 4,185,040(Ward et al.) for use in an olefin alkylation catalyst comprising Yzeolite.

U.S. Pat. No. 5,763,720 (Buchanan et al.), discloses a transalkylationprocess for conversion of C₉+ over a catalyst containing zeolitesillustrated in an extensive list including amorphous silica-alumina,MCM-22, ZSM-12, and zeolite beta, where the catalyst further contains aGroup VIII metal such as platinum.

U.S. Pat. No. 5,942,651 (Beech, Jr. et al.) discloses a transalkylationprocess in the presence of two zeolite containing catalysts. The firstzeolite is selected from the group consisting of MCM-22, PSH-3, SSZ-25,ZSM-12, and zeolite beta. The second zeolite contains ZSM-5, and is usedto reduce the level of saturate co-boilers in making a higher puritybenzene product.

U.S. Pat. No. 5,952,536 (Nacamuli et al.) discloses a transalkylationprocess using a catalyst comprising a zeolite selected from the groupconsisting of SSZ-26, A1-SSZ-33, CIT-1, SSZ-35, and SSZ-44. The catalystalso comprises a mild hydrogenation metal such as nickel or palladium,and can be used to convert aromatics with at least one alkyl groupincluding benzene.

U.S. Pat. No. 6,060,417 (Kato et al.), discloses a transalkylationprocess using a catalyst based on mordenite with a particular zeoliticparticle diameter and having a feedstream limited to a specific amountof ethyl containing heavy aromatics. Said catalyst contains nickel orrhenium metal.

Thus, many types of supports and elements have been disclosed for use ascatalysts in processes to transalkylate various types of aromatics intoxylenes. However, applicants have found that the specific size of thecatalyst used for these processes provides a surprising benefit whenreduced to a smaller than expected size, or shaped to increase theexterior surface area per gram of catalyst. Both of these sizelimitations effectively increase the diffusion of C₆ to C₁₀ aromaticsand enhance aromatic mass transfer rates to the surface.

SUMMARY OF THE INVENTION

A principal object of the present invention is to provide a process forthe transalkylation of alkylaromatic hydrocarbons. More specifically,the process of the present invention is directed to converting aromatichydrocarbons with improved yields of desired xylene isomers over asize-limited catalyst. This invention is based on the discovery thatspecific size limitations increase the exterior surface area per gram ofcatalyst and demonstrate improved activity in transalkylating toluenewith C₉+ aromatics.

Accordingly, a broad embodiment of the present invention is a catalystfor transalkylation of C₇, C₉, and C₁₀ aromatics to C₈ aromatics havinga trilobe shape with a maximum effective diameter of 1/16 inch (0.16cm). The catalyst is composed of a support, which can be selected fromthe group consisting of mordenite, beta, MFI, silica-alumina andmixtures thereof. The catalyst is also composed of an optional elementdeposited on the support selected from the group consisting of platinum,tin, lead, indium, germanium, rhenium, or any combination of theseelements. The catalyst also can contain a binder, which is preferablyalumina. The preferred support is mordenite.

In an alternate embodiment, the catalyst has a cylindrical shape with amaximum diameter of 1/32 inch (0.08 cm). Preferably the cylindricalshape can be characterized by a maximum average aspect ratio of 3.

The invention also encompasses a process for transalkylation ofaromatics comprising contacting a feedstream comprising C₇, C₉, and C₁₀aromatics with a catalyst at transalkylation conditions to produce aproduct stream comprising C₈ aromatics. Transalkylation conditionscomprise a temperature from about 200° C. to about 540° C., a pressurefrom about 100 kPa to about 6 MPa absolute, and a space velocity fromabout 0.1 to about 20 hr⁻¹. A preferred temperature range is from about300° C. to about 500° C.

These, as well as other objects and embodiments will become evident fromthe following detailed description of the invention.

BRIEF DESCRIPTION OF THE FIGURE

The FIGURE shows a trilobe shaped transalkylation catalyst of thepresent invention with a maximum effective diameter of 1/16″ (0.16 cm).

DETAILED DESCRIPTION OF THE INVENTION

The feedstream to the present process comprises alkylaromatichydrocarbons of the general formula C₆H_((6-n))R_(n), where n is aninteger from 0 to 5 and R is CH₃, C₂H₅, C₃H₇, or C₄H₉, in anycombination. Suitable alkylaromatic hydrocarbons include, for examplebut without so limiting the invention, benzene, toluene, ortho-xylene,meta-xylene, para-xylene, ethylbenzene, ethyltoluenes, propylbenzenes,tetramethylbenzenes, ethyl-dimethylbenzenes, diethylbenzenes,methylpropylbenzenes, ethylpropylbenzenes, triethylbenzenes,di-isopropylbenzenes, and mixtures thereof.

The feedstream preferably comprises benzene, toluene, and C₉ aromaticsand suitably is derived from one or a variety of sources. Feedstock maybe produced synthetically, for example, from naphtha by catalyticreforming or by pyrolysis followed by hydrotreating to yield anaromatics-rich product. The feedstock may be derived from such productwith suitable purity by extraction of aromatic hydrocarbons from amixture of aromatic and nonaromatic hydrocarbons and fractionation ofthe extract. For instance, aromatics may be recovered from a reformate.The reformate may be produced by any of the processes known in the art,with a process based on platinum containing L-zeolite being especiallypreferred for lower carbon number aromatic production. The aromaticsthen may be recovered from the reformate with the use of a selectivesolvent, such as one of the sulfolane type, in a liquid-liquidextraction zone. The recovered aromatics may then be separated intostreams having the desired carbon number range by fractionation. Thefeedstock should contain no more than about 10 mass-% non-aromatics; thecontent of benzene and C₈ aromatics is principally an economic decisionrelating to the efficiency of conversion to toluene from thesearomatics. When the severity of reforming or pyrolysis is sufficientlyhigh, extraction may be unnecessary and fractionation may be sufficientto prepare the feedstock. Benzene may also be recovered from the productof transalkylation.

A preferred component of the feedstock is a heavy-aromatics streamcomprising C₉ aromatics, thereby effecting transalkylation of tolueneand C₉ aromatics to yield additional xylenes. Benzene may also betransalkylated to yield additional toluene. Indan may be present in theheavy-aromatics stream although it is not a desirable component toeffect high yields of C₈ aromatics product. C₁₀+ aromatics also may bepresent, preferably in an amount of 30% or less of the feed. Theheavy-aromatics stream preferably comprises at least about 90 mass-%aromatics, and may be derived from the same or different known refineryand petrochemical processes as the benzene and toluene feedstock and/ormay be recycled from the separation of the product from transalkylation.

The feedstock is preferably transalkylated in the vapor phase and in thepresence of hydrogen. If transalkylated in the liquid phase, then thepresence of hydrogen is optional. If present, free hydrogen isassociated with the feedstock and recycled hydrocarbons in an amount offrom about 0.1 moles per mole of alkylaromatics up to 10 moles per moleof alkylaromatic. This ratio of hydrogen to alkylaromatic is alsoreferred to as hydrogen to hydrocarbon ratio. The transalkylationreaction preferably yields a product having an increased xylene contentand also comprises toluene.

The feed to a transalkylation reaction zone usually first is heated byindirect heat exchange against the effluent of the reaction zone andthen is heated to reaction temperature by exchange with a warmer stream,steam or a furnace. The feed then is passed through a reaction zone,which may comprise one or more individual reactors. The use of a singlereaction vessel having a fixed cylindrical bed of catalyst is preferred,but other reaction configurations utilizing moving beds of catalyst orradial-flow reactors may be employed if desired. Passage of the combinedfeed through the reaction zone effects the production of an effluentstream comprising unconverted feed and product hydrocarbons. Thiseffluent is normally cooled by indirect heat exchange against the streamentering the reaction zone and then further cooled through the use ofair or cooling water. The effluent may be passed into a stripping columnin which substantially all C₅ and lighter hydrocarbons present in theeffluent are concentrated into an overhead stream and removed from theprocess. An aromatics-rich stream is recovered as net stripper bottomswhich is referred to herein as the transalkylation effluent.

To effect a transalkylation reaction, the present invention incorporatesa transalkylation catalyst in at least one zone, but no limitation isintended in regard to a specific catalyst other than size and shape.Conditions employed in the transalkylation zone normally include atemperature of from about 200° C. to about 540° C. The transalkylationzone is operated at moderately elevated pressures broadly ranging fromabout 100 kPa to about 6 MPa absolute. The transalkylation reaction canbe effected over a wide range of space velocities, with higher spacevelocities effecting a higher ratio of para-xylene at the expense ofconversion. Weighted hourly space velocity (WHSV) generally is in therange of from about 0.1 to about 20 hr⁻¹.

The transalkylation effluent is separated into a light recycle stream, amixed C₈ aromatics product and a heavy-aromatics stream. The mixed C₈aromatics product can be sent for recovery of para-xylene and othervaluable isomers. The light recycle stream may be diverted to other usessuch as to benzene and toluene recovery, but alternatively is recycledpartially to the transalkylation zone. The heavy recycle stream containssubstantially all of the C₉ and heavier aromatics and may be partiallyor totally recycled to the transalkylation reaction zone.

One skilled in the art is familiar with several types of transalkylationcatalysts that may be suitably sized and shaped for use in the presentinvention. For example, in U.S. Pat. No. 3,849,340, which is hereinincorporated by reference, a catalytic composite is described comprisinga mordenite component having a SiO₂/Al₂O₃ mole ratio of at least 40:1prepared by acid extracting Al₂O₃ from mordenite prepared with aninitial SiO₂/Al₂O₃ mole ratio of about 12:1 to about 30:1 and a metalcomponent selected from copper, silver and zirconium. Friedel-Craftsmetal halides such as aluminum chloride have been employed with goodresults and are suitable for use in the present process. Hydrogenhalides, boron halides, Group I-A metal halides, iron group metalhalides, etc., have been found suitable. Refractory inorganic oxides,combined with the above-mentioned and other known catalytic materials,have been found useful in transalkylation operations. For instance,silica-alumina is described in U.S. Pat. No. 5,763,720, which isincorporated herein by reference. Crystalline aluminosilicates have alsobeen employed in the art as transalkylation catalysts. ZSM-12 is moreparticularly described in U.S. Pat. No. 3,832,449, which is incorporatedherein by reference. Zeolite beta is more particularly described in Re.28,341 (of original U.S. Pat. No. 3,308,069) which is incorporatedherein by reference. A favored form of zeolite beta is described in U.S.Pat. No. 5,723,710, which is incorporated herein by reference. Thepreparation of MFI topology zeolite is also well known in the art. Inone method, the zeolite is prepared by crystallizing a mixturecontaining an alumina source, a silica source, an alkali metal source,water and an alkyl ammonium compound or its precursor. Furtherdescriptions are in U.S. Pat. No. 4,159,282, U.S. Pat. No. 4,163,018,and U.S. Pat. No. 4,278,565, all of which are incorporated herein byreference.

A refractory binder or matrix is optionally utilized to facilitatefabrication of the catalyst, provide strength and reduce fabricationcosts. The binder should be uniform in composition and relativelyrefractory to the conditions used in the process. Suitable bindersinclude inorganic oxides such as one or more of alumina, magnesia,zirconia, chromia, titania, boria, thoria, phosphate, zinc oxide andsilica. Alumina is a preferred binder.

The catalyst also contains an optional metal component. One preferredmetal component is a Group VIII (IUPAC 8–10) metal, preferably aplatinum-group metal. Alternatively a preferred metal component isrhenium. Of the preferred platinum group, i.e., platinum, palladium,rhodium, ruthenium, osmium and iridium, platinum is especiallypreferred. This component may exist within the final catalytic compositeas a compound such as an oxide, sulfide, halide, or oxyhalide, inchemical combination with one or more of the other ingredients of thecomposite, or, preferably, as an elemental metal. This component may bepresent in the final catalyst composite in any amount which iscatalytically effective, generally comprising about 0.01 to about 2mass-% of the final catalyst calculated on an elemental basis. Theplatinum-group metal component may be incorporated into the catalyst inany suitable manner such as coprecipitation or cogellation with thecarrier material, ion exchange or impregnation. Impregnation usingwater-soluble compounds of the metal is preferred. Typicalplatinum-group compounds which may be employed are chloroplatinic acid,ammonium chloroplatinate, bromoplatinic acid, platinum dichloride,platinum tetrachloride hydrate, tetraamine platinum chloride, tetraamineplatinum nitrate, platinum dichlorocarbonyl dichloride,dinitrodiaminoplatinum, palladium chloride, palladium chloridedihydrate, palladium nitrate, etc. Chloroplatinic acid is preferred as asource of the especially preferred platinum component. Moreover, whenthe metal component is rhenium, typical rhenium compounds which may beemployed include ammonium perrhenate, sodium perrhenate, potassiumperrhenate, potassium rhenium oxychloride, potassium hexachlororhenate(IV), rhenium chloride, rhenium heptoxide, and the like compounds. Theutilization of an aqueous solution of perrhenic acid is highly preferredin the impregnation of the rhenium component. Rhenium may also be usedin conjunction with a platinum-group metal.

The catalyst may optionally contain a modifier component. Preferredmetal components of the catalyst include, for example, tin, germanium,lead, indium, and mixtures thereof. Catalytically effective amounts ofsuch metal modifiers may be incorporated into the catalyst by any meansknown in the art. A preferred amount is a range of about 0.01 to about2.0 mass-% on an elemental basis.

One preferred shape of the catalyst of the present invention is acylinder with a maximum diameter of 1/32 inch (0.08 cm). Such cylinderscan be formed using extrusion methods known to the art. They can becharacterized with an aspect ratio of height divided by diameter, suchthat a preferred maximum aspect ratio is 3.

Another preferred shape of the catalyst is one having a trilobal orthree-leaf clover type of cross section. This has been illustrated inthe FIGURE. The maximum diameter of the trilobe shape is defined bycircumscribing effectively a circle around the entire cloverleaf shape.Then using the diameter of that effective circle, the maximum diameterof the trilobe shaped catalyst is 1/16 in. (0.16 cm).

EXAMPLES

The following examples are presented only to illustrate certain specificembodiments of the invention, and should not be construed to limit thescope of the invention as set forth in the claims. There are manypossible other variations, as those of ordinary skill in the art willrecognize, within the scope of the invention.

Example One

Samples of catalysts comprising mordenite were prepared for comparativepilot-plant testing by the forming process called extrusion. Typically,2500 g of a powder blend of 25% alumina (commercially available underthe trade names Catapal™ B and/or Versal™ 250) and 75% mordenite(commercially available under the trade name Zeolyst™ CBV-10A, which hasbeen ammonium exchanged to remove sodium) was added to a mixer. Asolution was prepared using 10 g nitric acid (67.5% HNO₃) with 220 gdeionized water and the solution was stirred. The solution was added tothe powder blend in the mixer, and mulled to make a dough suitable forextrusion. The dough was extruded through a die plate to form extrudateparticles. The extrudate particles were dried on a belt calcineroperating with a first zone at 340° C. for about 45 minutes and a secondzone at 570° C. for about 90 minutes.

Based on three different die plates, three differently shaped extrudatecatalyst particles were prepared. Catalyst A was a 1/16 inch (0.16 cm)cylinder, which was prepared to match the state of the art. Catalyst Bwas a 1/16 inch (0.16 cm) trilobe, as shown in the FIGURE, which wasprepared to demonstrate an embodiment of the invention. Catalyst C was a1/32 inch (0.08 cm) cylinder, which was prepared to demonstrate anotherembodiment of the invention.

Example Two

Catalysts A, B, and C were tested for aromatics transalkylation abilityin a pilot plant using three different feed blends to demonstrateeffectiveness of C₉+ conversion as compared to toluene conversion. Thetest consisted of loading a vertical reactor with catalyst andcontacting the feed at 400 psig (2860 kPa abs) under a specified spacevelocity (WHSV) and hydrogen to hydrocarbon ratio (H₂/HC). Activity wasdetermined by targeting an overall conversion of feedstock based on areactor temperature measurement. Thus, a lower temperature indicates acatalyst with better activity.

These three feeds compared toluene against feeds containing C₉+. The C₉+component contained about 70 wt-% C₉ aromatics and about 30 wt-% C₁₀aromatics. The results from this test are summarized in the table belowindicating equivalent start of run activity at 35 wt-% overallconversion for a feed blend consisting of 15 wt-% C₇. Also included areresults indicating start of run activity at 50 wt-% overall conversionfor feed blends consisting of 50 wt-% C₇ and 100 Wt-% C₇.

TABLE Catalyst Catalyst Feed Blends A B Catalyst C {15 wt-% C₇ and 85wt-% C₉+}¹ 454° C. 417° C. 415° C. (trial 1) 427° C. (trial 2) {50 wt-%C₇ and 50 wt-% C₉+}² 417° C. 405° C. 406° C. {100 wt-% C₇}³ 397° C. 394°C. 395° C. ¹Activity test at 35% conversion, 4.0 hr⁻¹ WHSV, and 4:1H₂/HC ²Activity test at 50% conversion, 1.8 hr⁻¹ WHSV, and 6:1 H₂/HC³Activity test at 50% conversion, 4.0 hr⁻¹ WHSV, and 6:1 H₂/HC

The data indicated that catalysts B and C had better activity than thestate of the art catalyst A, and a difference greater than 5° C. wasgenerally considered to be significant between catalysts. Moreover, thedata indicated that the activity difference increased as the presence ofthe heavier aromatic blend component, as exemplified by C₉+, wasincreased.

1. A catalyst for transalkylation of C₇, C₉, and C₁₀ aromatics to C₈aromatics, comprising a component selected from the group consisting ofa mixture of mordenite and MFI topology zeolite and a mixture ofmordenite, MFI topology zeolite and silica-alumina; an optional elementdeposited on the component selected from the group consisting ofplatinum-group metal, tin, lead, indium, germanium, rhenium, nickel,iron, cobalt or a combination thereof; and the catalyst having a trilobeshape with a maximum effective diameter of 1/16 inch (0.16 cm).
 2. Thecatalyst of claim 1 wherein the catalyst further comprises a binder. 3.The catalyst of claim 2 wherein the binder is alumina.
 4. The catalystof claim 1 wherein the component is a mixture of mordenite and MFItopology zeolite.
 5. A catalyst for transalkylation of C₇, C₉, and C₁₀aromatics to C₈ aromatics, comprising a component selected from thegroup consisting of a mixture of mordenite and MFI topology zeolite anda mixture of mordenite, MFI topology zeolite and silica-alumina; anoptional element deposited on the component selected from the groupconsisting of platinum-group metal, tin, lead, indium, germanium,rhenium, nickel, iron, cobalt or a combination thereof; and the catalysthaving a cylindrical shape with a maximum diameter of 1/32 inch (0.08cm).
 6. The catalyst of claim 5 wherein the cylindrical shape ischaracterized by a maximum average aspect ratio of
 3. 7. The catalyst ofclaim 5 wherein the catalyst further comprises a binder.
 8. The catalystof claim 7 wherein the binder is alumina.
 9. The catalyst of claim 6wherein the component is a mixture of mordenite and MFI topologyzeolite.
 10. A catalyst for transalkylation of C₇, C₉, and C₁₀ aromaticsto C₈ aromatics, comprising a component selected from the groupconsisting of a mixture of mordenite and MFI topology zeolite and amixture of mordenite, MFI topology zeolite and silica-alumina; anelement deposited on the component selected from the group consisting ofplatinum-group metal, tin, lead, indium, germanium, rhenium, nickel,iron, cobalt or a combination thereof; and the catalyst having a trilobeshape with a maximum effective diameter of 1/16 inch (0.16 cm).
 11. Thecatalyst of claim 10 wherein the catalyst further comprises a binder.12. The catalyst of claim 11 wherein the binder is alumina.
 13. Thecatalyst of claim 10 wherein the component is a mixture of mordenite andMFI topology zeolite.
 14. A catalyst for transalkylation of C₇, C₉, andC₁₀ aromatics to C₈ aromatics, comprising a component selected from thegroup consisting of a mixture of mordenite and MFI topology zeolite anda mixture of mordenite, MFI topology zeolite and silica-alumina; anelement deposited on the component selected from the group consisting ofplatinum-group metal, tin, lead, indium, germanium, rhenium, nickel,iron, cobalt or a combination thereof; and the catalyst having acylindrical shape with a maximum diameter of 1/32 inch (0.08 cm). 15.The catalyst of claim 14 wherein the cylindrical shape is characterizedby a maximum average aspect ratio of
 3. 16. The catalyst of claim 14wherein the catalyst further comprises a binder.
 17. The catalyst ofclaim 16 wherein the binder is alumina.
 18. The catalyst of claim 14wherein the component is a mixture of mordenite and MFI topologyzeolite.